"We are very encouraged by this data," says study researcher Heidi M. Blanck, PhD, of the CDC in Atlanta. "It's pretty exciting and a nice turning of the tide. But we have to stay vigilant or it will go in the other direction."

Researchers looked at data on 27.5 million children aged 2 to 4 from 1998 to 2010. These children were from 30 states and Washington, D.C. Many were eligible for government assistance.

The rate of child obesity rose from 13.05% in 1998 to 15.21% in 2003. But it fell to 14.94% in 2010.

The rate of extreme child obesity declined from 2.22% in 2003 to 2.07% in 2010, the study shows.

The findings appear in the Journal of the American Medical Association.

What makes the data even more promising is that many of the national initiatives aimed at lowering rates of childhood obesity hadn't been started or were not at full force during most of the study period, Blanck says.

For example, efforts aimed at making it easier for new moms to breastfeed are just now gaining traction. Breastfeeding has been shown to help prevent obesity. There are also new programs that help people on food stamps purchase healthier foods.

Fighting Obesity With Lifestyle Changes

There's also a lot that families can do in their own homes to encourage healthy lifestyles. These include getting more physical activity during the day and less screen time. "Walk the family dog together to get exercise," Blanck says.

Also, get rid of sugary drinks and beverages in the home, and make fruits and vegetables available. "We know that childhood obesity tracks into adulthood, so it's important to make these changes early and maintain them," she says.

"The news is definitely encouraging," says Leslie Lam, MD. He is a doctor at The Children's Hospital at Montefiore Medical Center in New York City.